I am using volley library to perform network operations. On Application launch, I hit the service, I want to stop all the operations until i get the response from the service.
So i want to perform this synchronously. As I am using Volley which by default works in a separate thread. So how can i do this.
I have created custom Interface/listener to handle this, but does Android provide some way to achieve this.
I have done following.
Splash Activity implements an interface, and it goes to Main Activity after data is loaded
#Override
public void onContainerLoaded() {
//startActivity(MainActivity)
}
Even if you want to, you should definitely never EVER run any network-related task synchronously.
What you can do instead is starting your activity normally, and replace your layout with a progressbar logo, that is set to visibility.gone when your task is completed.
EDIT : By the way, if you are just starting your app and you haven't done anything concrete yet, I would recommend you to use an AsyncTask instead of Volley, which is often causing layer-coupling mistakes.
Use some event bus such as Otto
Create an event, make your main activity subscribe to the event using the event bus, start your operation, display a "Loading..." or something ProgressDialog in your main activity. From your worker thread when it completes send an event to your main activity. Make your main activity close the "Loading" dialog when it receives the event,
I guess a better question would be why you want to force it on the main thread?
As far as I know, volley won't let you do that but you might be able to if you make your own network operation. After Honeycomb, you will get a NetworkOnMainThreadException so you will need to override the policies.
Related
I have currently the following problem:
I got a server that provides and API via Google Protobuf. A Program (in this case an Android App) can request informations. I have an Activity in Android that will request Informations in the Background via a Runnable, which will then process the network request and dispatch to a function on the mainthread to update the UI with the new informations. Therefore I give the runnable a final interface with the function to dispatch which is implemented by the Activity. Now as the network stuff happens in the background and the UI should not block (e.g. with a Loading Spinner) I dont know what happens when the user switches to another Activity while the Runnable is still active. Will it still dispatch properly even if there is another Activity active? What is good design practice to solve this.
Of course I thought about adding a variable to the Runnable to mark it as dont dispatch, but there still could be race conditions (it gets dispatched while the user hits the back button, which would already have the dispatched function in the queue for the mainthread before marking the Runnable as aborted).
If you need any additional informations, please ask, I am happy to provide them.
I am learning Android app development from Udacity.com by Google engineers and they said,
"It is not a good idea to use 'AsyncTask' as it is not attached to an activity life cycle. The virtual machine will hold on to the activity object as long as the Asynctask is running, even after Android has called onDestroy( ) method for the activity and expect it to be discarded.
If you rotate your phone, the behavior is to destroy the current activity and instantiate a new one. The naive AsyncTask implementation now has two threads trying to do the same update. So it is not the best pattern for a potentially very long running background operation , such as fetching from web services. If you leave the app, the asyncTask will run as long as as the process is kept alive , but will run at a lower priority, and your process will be the first thing to be killed if the device needs more resources. "
1) If using AsyncTask is disadvantageous why was it created? What would have been the design philosophy or the cause to create it in spite of having services(or something similar to achieve same kind of functionality)?
2) What are the situations where Asynctask should be used for betterment compared to Services/similar options available in Android?
3) What are the situations/places Asynctask should never be used?
Please do not downvote this question. I searched Stackoverflow and I couldn't find a similar question.
Advantages of AsyncTask
Provides generic solution for all network calls
Publish progress to UI while executing.
Run Asynchronously
Easy to maintain and read.
Problems in AysncTask
When you rotate your screen, Activity gets destroyed, so AsyncTask will not have a valid reference to publish data from onPostExecute(). In order to retain it, you need to usesetRetainState(true) if calling from fragment or onConfigChanges() if calling from activity method of an activity.
If activity gets finished, AsyncTask execution will not cancelled automatically, you need to cancel them else they will keep on running in the background.
If any exception occurs while performing network task, you need to handle them manually.
Whereas AsycTask, Services, IntentService, Threads all run on different threads and all serve different purpose.
please read more detail here.
So you need to decide when to use which component while performing non UI operations.
I'm trying to design an application that does two different tasks in parallel
each task start executing when the user presses a button in the activity "so I have three Activities two of them should do some tasks and the third one should collect the result".
When the user presses the button on the activity it will invoke a thread and then will Load the next Activity
In the third activity I have a button "I called it Send Button " that should stay inactive or disabled until all threads finish their work so at that moment it will be enabled and this activity contains plain text to show the result from these two threads and when the user presses this button it will send the information in the plain text to a web site.
My questions are : how can I run Threads in a different activity and send their result to another one? and how can I make that "Send Button" disabled until all threads finish their work.
I tried to make a while loop using a global variable in the onCreate method in the Third activity but it crashes the application and the activity didn't start up
You have two options to do a long running background task:
Using a thread which does your background work, with an singelton to access the results
Using a services which does the calculations
Depending on your actual use case the service is the first choice.
Use an Activity only when you need user interaction to your application. Else you can invoke both the threads using AsyncTask for your jobs(If you want the system to handle the worker threads for you. And unless you do not do any config changes on the fly -> performance hit).
Please keep in mind that, you should use AsyncTask only when the background jobs run for dew seconds. If you have a long running job, then use a service with a custom thread.
Hope this helped.
You can use AsyncTask. AsyncTask is one Class which is used to perform background processes without having threads. You can easily check the process is completed or not. Check this Tutorial. This can help you to understand how to run background process using an AsyncTask.
I searched through most answers here and all suggest we add a flag to the intent to kill old activities. The problem is my activity only receive intents from other app and has no control over it.
More specifically, my activity receive an intent to load a picture, then it uses Asynctask to load and do some complicated background processing of that picture, say, may be 2 minutes.
If the user at this moment back out (assuming that only onStop is called, not yet onDestroy) and share another picture to the app , this will start a new activity, and the previous activity cannot be accessed, but its Asynctask hold up the thread so that my new activity just freeze without starting its own Asynctask.
(I later tried the parallel thread executor, but this doesn't stop the old thread from running, thus consuming computational resources).
Any idea what I should do?
(I don't want to stop the task in onStop as this is to easy to be called. But I do want to stop the task if new picture is shared, since it is no longer needed.)
(The Asynctask will spit out a huge array of self-defined Objects declared in the main activity, and thus the activity gets immediate updates of the result from the background process, and the UI updates immediately after onPostExecute is called.)
EDIT:
It seems that your problem is that you're trying to do all this image processing work in asynctasks launched by your activity. Have you considered changing your app architecture to rely all this background processing to a service?
You can use the activity to show some UI information while you process the image in your service, or if you don't need this UI just simply communicate with the service (through broadcast, for example) to provide it the image and let the service show some information of the process through notifications.
If you don't want to keep your activity alive when you exit it you can use
android:noHistory="true" in your activity declaration at the manifest
More info here
This is the workaround, and seems it is working very well for the moment:
After getting a sharedpreference prefs, do this in onCreate:
prefs.edit().putBoolean("ForceClose", true).commit();
In the onPreExecute() of the AsyncTask, put:
prefs.edit().putBoolean("ForceClose", false).commit();
In the doInBackground() of the AsyncTask, constantly check for
if (prefs.getBoolean("ForceClose", false))
cancel(true);
and call finish() in onCancelled() to finish off the activity.
I have a sync service using AsyncTask. Due to its objective (sync), I prefer to block the user and show him a progressdialog. (And error if exists)
Another difficulty is that I have about 8 AsyncTask running simultaneously. So I can't do a simple call to the progress dialog page when I begin the work and a close when it's finished. It's more complex.
Can someone help me with that task ?
Regards
onPreExecute(), onProgressUpdate(Progress...) and onPostExecute(Result) in AsyncTask are invoked on the UI thread. You can use these to display a progress bar, update it as the syncing progresses and hiding it when the work is finished.
As to the 8 simultaneous async tasks, do you really need 8 concurrent tasks? Can't you run them sequentially on one background thread using a single AsyncTask?
In the first place the point of the Service is that you don't need/want to block user to do stuff because it happens in the background. To that aspect, a Service doesn't have a UI thread, so if you want a progress bar shown in your Activity you'll have to send an Intent back to your activity (using broadcast receivers), such that you can switch the progress bar on/off and do other magic.
I would not recommend blocking the user though, because the tasks you are doing might take a very long time, giving a nasty user experience. You might even want to reconsider using a Service at all (if the data you are fetching is only used locally; for example fetch the latest twitter messages or something) and just go with an ASyncTask in your Activity, unless the data your Service fetches is used in other parts of your app as well (widgets for example) and you want that data available even if the activity isn't running.
You can make use of progress dialog to show wait cursor kinda thing.
Also you can imitate the concept of CountDownLatch in your application to dismiss the cursor. Like you can have a static function in a class like updateTaskComplete and update a static counter. And once the counter is equal to number of async task then in the function updateTaskComplete cancel the progress cursor. I mean you have to do something on this line.